Public-health officials are enthusiastic about the new, single-shot COVID-19 vaccine from Johnson & Johnson, despite its having a somewhat lower efficacy at preventing symptomatic illness than other available options. Although clinical-trial data peg that rate at 72 percent in the United States, compared with 94 and 95 percent for the Moderna and Pfizer-BioNTech vaccines, many experts say we shouldn’t fixate on those numbers.
